Various mechanisms have been proposed heretofore for radially expanding an annular workpiece. Examples of such prior proposals are disclosed in the following U.S. Pat. Nos. 72,904, Rees; 629,444, Hem; 752,153, Grotnes; 980,399, Bauroth; 1,039,885, Bauroth; 1,058,669, Goddard; 1,982,400, Reim; 2,089,476, Grotnes; 1,779,377, Swern; 2,413,103, Forbes; 2,931,416, Krise; 3,109,477, Avera; 1,067,115, Hufford; and 1,285,982, Goodard.